In a semiconductor device manufacturing process, a plasma etching apparatus that etches a substrate such as a semiconductor wafer (simply referred to as “wafer” hereinafter) by irradiating plasma on the wafer may be used as an apparatus for processing the wafer.
In plasma etching, a gas containing fluorine, chlorine, and oxygen, for example, may be used as a processing gas that is turned into plasma. Plasma includes active species such as charged particles (referred to as “ion” hereinafter) and neutral particles (referred to as “radicals” hereinafter), for example. The surface of a wafer reacts with the ions and radicals contained in the plasma to prompt the generation of reaction products, and etching of the wafer progresses as the reaction products are volatized.
In recent years, the diameter of wafer holes are becoming larger. As the wafer hole diameter is enlarged, it becomes increasingly difficult to ensure in-plane uniformity of the depth and line width (critical dimension: CD) of bottom portions of holes (and trenches) within a wafer plane in an etching process.
In this respect, Patent Document 1 discloses a technique for controlling the concentration distribution of radicals at a center region and a peripheral region within a wafer plane by adjusting the supply rate of processing gas supplied from an upper electrode.    Patent Document 1: Japanese Patent No. 4358727